LASAIR II (low end 0.1um) "Used":
http://www.ebay.com/itm/Airborne-Particle-Counter-LASAIR-II-110-0-1-m-Particle-Measuring-Systems-/261060009276
Since zeig used the phrase "Air Quality" it must be for PM20 and PM2.5 measurements of living areas. The "dust sensor" is just a good as any low-end system since the discrimination of sizes on the 2-3 channel systems is highly suspect.